1. Field of the Invention
The invention relates to a method for the permanent connection of two components, of which at least one component comprises an electrically nonconductive material, by soldering employing a glass or metal solder as the solder material, in which a layer system providing adhesion is applied to at least one of the two components, onto which the solder material is applied, which is brought indirectly or directly into contact with the other components and is heated to a soldering temperature characteristic for the solder material and results in a permanent soldered connection between both components after cooling.
2. Description of the Prior Art
For manifold applications, for example, in the field of optics or measuring technology, permanent connections must be produced between components made of different or similar materials, such as glass to glass or glass to metal, on which various demands are made. For example, connections of this type must be mechanically robust and resistant to external environmental influences, such as electromagnetic radiation, moisture, and temperature, to name only a few. In order to meet these demands, soldered connections have proven to be particularly suitable in order to connect two components permanently to one another, of which at least one component comprises an electrically nonconductive material, preferably a glass-like material such as quartz glass, float glass, for example, single-pane safety glass, composite safety glass, and partially tempered safety glass, or a ceramic material. For this purpose, metal solder materials or glass solders which are known per se are melted and applied to the surfaces of the components to be connected to one another, in order to be used as an adhesive and binding layer between the two components. However, it has been shown that the known solder materials only inadequately wet the surfaces of electrically nonconductive materials in particular and also many metal materials. That is, they do not form an adhesion-stable surface connection to the components, so that the surfaces of the components to be joined with one another must first be coated using a solderable layer which forms a sufficient adhesive connection to the particular surface of the components. For this purpose, layer systems which comprise at least three layer components are frequently used, which are applied to the surface of the particular components to be connected for reasons of improved adhesive capability and simultaneously improved soldering properties. The typical three-layered layer systems comprise an adhesive layer to be applied directly to the component surface(s), a solderable layer to be applied thereon, and finally an oxidation protective layer to be applied to the solderable layer.
The layer sequence is typically produced in the course of sputtering methods or galvanic deposition methods which are preferably performed in the context of a pretreatment, in which the multicomponent layer system is applied to each of the surfaces of the components to be joined to one another. Finally, the solder material is applied between the coated join surfaces, which results in an adhesion-stable soldered connection between the two components through heating to a temperature characteristic for the particular solder material which is the so-called melting temperature, and subsequent cooling. Depending on the type of material of the components to be joined to one another, metal solders or glass solders are used as the solder material.
Thus, for example, a soldering method for optical materials on metal frames is disclosed in EP 0 901 992 A2, in which an adhesive layer comprising CrAl or TiW is applied at least to the surface of the component comprising the optical material which is preferably quartz glass, onto which a diffusion barrier layer in the form of pure nickel is sputtered. In addition, a gold layer, used as an oxidation protective layer, is applied to the layer composite. The surface of the metal frame, in contrast, is only provided with a wetting auxiliary layer comprising nickel or copper, on which the solder material which is tin or an indium alloy, is applied. The soldering material melts at soldering temperatures below 300° C. and which forms an intimate soldered connection with excellent adhesive strength to the layer system applied to the glass material after corresponding cooling.
A method for producing window elements which are solderable to provide a hermetic sealed in a housing may be inferred from DE 10 005 024 512 B3. An aluminum layer and/or titanium or a titanium alloy is applied as the adhesive layer. In the described method, platinum, iron/nickel, nickel, or palladium, which is coated by an oxidation protective layer comprising gold, is used as the solderable layer.
A method for connecting an optical glass fiber to a metal mount in the course of a soldered connection is described in US Published Application 2003/0174999 A1. The glass fiber is provided with a layer system which primarily has an adhesive layer, which comprises WTi, CrAu, Cr, NiCr, onto which a solderable layer is applied, comprising nickel or platinum, which is finally coated using a gold oxidation protective layer.
A fluxless soldering method for connecting a glass part to a metal part may be inferred from DE 692 18 004 T2. A layer system is applied to the glass part, which has titanium as the adhesive layer, nickel as the solderable layer, and a nickel-boron alloy or gold as the oxidation protective layer.
A method for connecting ceramic and metal bodies may be inferred from DE 34 85 859 T2. A compound made of an oxide and a metal is applied to the surface of the ceramic body using spray coating or ion plating as the adhesive layer, which forms a metallurgical connection to the ceramic body in the course of the heating. The joining to the metal body is subsequently performed using hard soldering.
A semiconductor part having semiconductor part components embedded in plastic housing compound may be inferred from DE 10 2005 028 704 A1. The semiconductor part components are joined to the plastic housing using an adhesive layer without further addition of a solder material and the adhesive layer has nanoscale surface structuring, by which the joining to the particular joint partner is ensured using a positive connection.
If adhesive layers which comprise metal are used, as is entirely the case in the above-mentioned cited art, the disadvantage is that the thermal expansion coefficients of the metal layer and the material to which the components are to be joined typically differ strongly. In addition, the adhesive strength of metal layers on electrically nonconductive substrate surfaces, such as glass-like or crystalline materials, is frequently significantly less than on metal substrate surfaces. These factors may result in the formation of high transient mechanical internal tensions within the layer composite or the substrate surface upon heating of the soldering composite, such as tensile or compressive stress, which already result in cracking in the layer or in the substrate material or the detachment of the particular adhesive layer from the substrate surface during soldering in the worst case. Strongly pronounced mechanical internal tensions may also occur in the interface between the solder material and the applied layer system upon cooling of the solder, which may result in layer failure. It is obvious that the strength of the solder composite is reduced by internal tensions inherent to the layer and in the worst case can already result in failure of the solder composite upon the action of slight mechanical strains.
A further disadvantage of adhesive layers comprising metals is that as a consequence of the comparatively high reflection values for IR radiation, the metal layers represent a heat barrier. It becomes more difficult to introduce the heat required for melting the solder material efficiently into the solder material, and/or higher heating powers are required, which may result in higher thermal strains of the participating components and/or longer processing times.